Dima AlMekdad (Presenter)
King's College London & LGC
Bio: Dima AlMekdad is a Research Analyst in the Science and Innovation Division at LGC and a part time PhD student at King's College London. Dima’s research is focussed on the development of reference measurement procedures for clinically relevant compounds in biological fluids, including immunosuppressant drugs in whole blood and metanephrines in plasma and urine for the diagnosis of pheochromocytoma and paraganglioma. Originally Dima trained to be a pharmacist, obtaining a BSc in Pharmacy and Pharmaceutical Chemistry from University of Kalamoon in 2010, followed by an MSc in Analytical Toxicology from King’s College London in 2012.
Authorship: Dima AlMekdad(a,b), Mark Parkin(a), Leon Barron (a), Chris Mussell(b)
(a) Analytical & Environmental Sciences Division, King's College London, 4th Floor, Franklin-Wilkins Building, 150 Stamford Street, London SE1 9NH (b) Science & Innovation Division, LGC, Queens Road, Teddington, Middlesex, TW11 0LY
| Short Abstract The immunosuppressant drug tacrolimus requires Therapeutic Drug Monitoring. External Quality Assurance data for tacrolimus demonstrates that there is currently an unacceptable inter-laboratory variability. LGC has developed a Reference Measurement Procedure (RMP) for tacrolimus in whole blood which has been applied to the characterisation of Certified Reference Materials and assigning target concentrations in laboratory intercomparisons. This RMP has been adapted for the evaluation of a novel Volumetric Absorptive Microsampling (10 µL) device. Preliminary data using a ‘wet’ device provided fit for purpose data. However use of dried tips resulted in bias which could not be accounted for and requires further investigation. |
Long Abstract
Introduction
The narrow therapeutic range of the immunosuppressant drug tacrolimus is further complicated by both inter and intra-patient variability of absorption, distribution, metabolism, and excretion of the drug. Consequently it is necessary to Therapeutic Drug Monitor (TDM) tacrolimus; whereby the transplant patient will regularly have a venous blood sample taken and the concentration levels of tacrolimus quantified and the dose adjusted accordingly. Patients will undergo TDM for the rest of their lives.
Currently there is an unacceptable variability between hospital laboratories analytical results when performing tacrolimus TDM. The reasons for this variability include differences in assay types and calibrants used. High accuracy reference measurement procedures have been developed at LGC based on isotope dilution mass spectrometry.
Methods
A high accuracy Reference Measurement Procedures (RMP) has been developed using LC-MS/MS in conjunction with an exact matching isotope dilution calibration protocol. This methodology has been applied successfully to the assignment of reference mass concentrations to certified reference materials and global external quality assurance schemes, regularly achieving sub 3% expanded measurement uncertainty at 95% confidence level.
Recently, we have adapted this methodology to evaluate the MitraTM low volume (10 µL) blood sampling devices
Pooled patient blood sample and matrix matched calibrants were used. Samples were prepared by red blood cells lysis step via zinc sulfate followed by protein precipitation and finally cleaned up by non-polar solid phase extraction. Extracts were then analysed using Thermo Vantage TSQ LC-MS.
LC column used was Thermo Hypersil Gold (C18) column at 50 °C with a gradient LC of methanol and water. Selected reaction monitoring (SRM) transitions used were 826.3>616.2/415.18 m/z and 831.3>621.2/420.18 m/z for tacrolimus and isotope labelled tacrolimus internal standard, 2 SRMs were acquired for each compound.
Preliminary data
The RMP developed was used to assign reference concentrations to a candidate ‘higher order’ certified reference material of pooled patient blood. A reference value was assigned to the tacrolimus in pooled patient blood reference material with an expanded measurement uncertainty (at the 95% Confidence level) of <5%. The RMP is also to be used for stability and commutability testing of the material and to assign reference values for samples used for global inter-laboratory proficiency testing.
Additionally the RMP developed has been adapted to evaluate a novel micro-sampling device, which instead of requiring venous drawn blood, absorbs 10 µL of blood generated via a finger prick device. Should this Volumetric Absorptive Microsampling ‘VAMS’ device deliver accurate measurements for TDM, it would enable home sampling by the patient.
The VAMS device seems to provide good data within 10% of reference value of the patient reference material when used without drying the blood. However, a bias was observed when using the device with drying the blood for 24 hours. Further work is required to know whether the source of bias is due to the device or an unknown source of experimental bias.
It is hoped that continued provision of reference measurement services will enable laboratories to identify sources of bias and imprecision and ultimately achieve standardisation of laboratory analysis.
Conclusions
- High accuracy RMP was developed
- Provision of CRMs will enable standardisation of routine hospital tests and
* Reducing variability between hospital laboratories
* Ultimately improved patient welfare including extension of transplant organ lifetimes.
• RMP adapted to evaluate microsampling device
• Further work is still required to remove sources of bias and imprecision identified in the initial evaluation before the device can be implemented routinely.
References & Acknowledgements:
• The work described in this poster was funded by the UK National Measurement System.
• Prof. David Holt, ASI, St. George’s Hospital, University of London, UK
• Dr. James Rudge, Phenomenex, UK
• Some of the graphs used in the poster are adapted from mindthegraph.com
| Description | Y/N | Source |
| Grants | no | |
| Salary | yes | Salary - LGC |
| Board Member | no | |
| Stock | no | |
| Expenses | no |
IP Royalty: no
| Planning to mention or discuss specific products or technology of the company(ies) listed above: | no |